title: Photochemical coupling reactions between Fe(III)/Fe(II), Cr(VI)/Cr(III), and polycarboxylates: inhibitory effect of Cr species.
abstract: The roles of chromium species on photochemical cycling of iron and mineralization of polycarboxylates are examined in the presence of Cr(VI) or Cr(III) at pH 2.2-4.0. Under UV irradiation, Cr(III) altered the redox equilibrium of iron species, leading to the shift of the photosteady state toward Fe(II). After a longer time of illumination, total organic carbon (TOC) approached a steady state in the presence of Cr(III) or Cr(VI), whereas oxalate was thoroughly mineralized in the absence of Cr species. The TOC of steady state was closely related to the kind of polycarboxylates, Cr species dosages, pH and O2 atmosphere, but hardly affected by more addition of Fe(III). ESI-MS data indicates that several Cr-oxalate complexes formed in the photochemical reactions, which are responsible for protecting oxalate against further oxidation. A mechanism is proposed for the inhibitory effect of Cr species on oxidation of oxalate and Fe(II). The present study may provide a new insight into the dual environmental effects induced by Cr contaminants especially at heavily chromium-contaminated and dissolved organic matter (DOM)-rich sites.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Wang
authors.forename: Wanhong
authors.initials: W
authors.lastname: Ma
authors.forename: Chuncheng
authors.initials: C
authors.lastname: Chen
authors.forename: Jincai
authors.initials: J
authors.lastname: Zhao
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004777:Environment; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals / Q000737:chemistry; D008956:Models, Chemical; D010070:Oxalates / Q000737:chemistry; D010084:Oxidation-Reduction / Q000528:radiation effects; D010100:Oxygen / Q000737:chemistry; D055668:Photochemical Processes / Q000528:radiation effects; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D002264:Carboxylic Acids; D008903:Minerals; D010070:Oxalates; D002857:Chromium; D007501:Iron; D010100:Oxygen